Patterned Superhydrophobic Surfaces: Toward a Synthetic Mimic of the Namib Desert Beetle

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By Sung Hoon Kang


Title: Patterned Superhydrophobic Surfaces: Toward a Synthetic Mimic of the Namib Desert Beetle

Reference: L. Zhai, M. C. Berg, F. C. Cebeci, Y. Kim, J. M. Milwid, M. F. Rubner, and R. E. Cohen, Nano Lett. 6, 1213-1217 (2006).

Soft matter keywords

superhydrophobic surface, hydrophilic pattern, contact angle, Namib desert beetle

Abstract from the original paper

The present study demonstrates a surface structure that mimics the water harvesting wing surface of the Namib Desert beetle. Hydrophilic patterns on superhydrophobic surfaces were created with water/2-propanol solutions of a polyelectrolyte to produce surfaces with extreme hydrophobic contrast. Selective deposition of multilayer films onto the hydrophilic patterns introduces different properties to the area including superhydrophilicity. Potential applications of such surfaces include water harvesting surfaces, controlled drug release coatings, open-air microchannel devices, and lab-on-chip devices.

Soft matter example

In the Namib Desert where there is limited water source for plants and animals, there are very interesting creatures that have unique ways to collect water from the atmosphere. For example, the Stenocara beetle utilizes its wings with hydrophilic/superhydrophobic patterns to acquire water from fog-laden wind. At dawn, the Stenocara beetle leans its body toward the wind to collect small water droplets in the fog. Then, these small water droplets coalesce and become bigger droplets. When the droplets reach certain sizes, they roll down into the beetle's mouth. Parker and his colleagues reported that the structure of the beetle's back provided this unique ability to collect water [1]. According to their study, the beetle's back has an array of hydrophilic bumps with ~ 100 um in diameter on a superhydrophobic background. As a result, small water droplets in a fog are collected on the hydrophilic area and coalesce. When the weight of the droplet is big enough to overcome the adhesion forces of the hydrophilic region, it is detached from the surface and rolls down the superhydrophobic surface to the mouth of the beetle. In addition to this example of water collection, patterned surfaces with different wetting properties can be useful for many applications including microfluidic channels and rapid evaluation of complex bioactivities [2-4].

References

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